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Actual field of view (deg) = linear sensor (or film) width (mm) x 57.3 / focal length (mm).
In your case you have 4.6 x 57.3/1200 = 0.220 deg. and 4.0 x 57.3 / 1200 = 0.191 deg.
By using the same CCD on a telescope that has half the focal length will double your field of view as will doubling the CCD sensor size
Multiply by 60 to convert deg field of view to minutes, eg 0.22 x 60 = 13.2min. Multiple again by 60 to get field of view in seconds. (or multiply deg x 3600). Field expressed in minutes is useful for imaging galaxies and other deep sky objects and field expressed in seconds is useful for imaging planets.
In the days of film photographic magnification was related to that of a 50mm camera lens giving a magnification of one on 35mm (36 x 24mm) film). Therefore 1200mm focal length = 1200/50 = 24x magnification. If you had a full size CCD sensor matching film dimensions you could say your magnification is 24x compared to a standard 50mm lens. Since cameras have all different sized sensors and lenses multiplying factors are often referred to to be able to compare to a 50mm lens/35mm system. Most DSLR have a sensor 1.5x smaller than a film camera and therefore the multiplying factor is 1.5x. Referring to magnification is really meaningless for photo work and field of view can always be calculated by the above formula.
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